1. Field of the Invention
The present invention relates generally to medical devices and systems, and more particularly to medical devices for measuring skin characteristics that can vary on a patient-by-patient basis.
2. Description of the Related Art
The selectivity of the input impedance of an electronic system used in a medical environment is an important, though somewhat under emphasized feature of the overall monitoring device. As the sensitivity of electronic monitoring systems increase, it becomes increasingly important to consider the inaccuracy of measurements created by offset and gain errors caused by unknown or changing skin/electrode impedances. The effect is often significant enough to create an inability to monitor important electrical events during medical procedures. In several medical monitoring applications, an independent measurement of the patient skin/electrode impedance is made before initiation of electrical monitoring, to attempt to correct for the anticipated error caused by the impedance uncertainty. Even in the event of a pre-monitoring impedance measurement, no hardware or software solution exists to correct for the induced error. Furthermore, it has been established that the skin/electrode impedance can, and often does, change during an extended monitoring process. The present invention discloses a hardware/embedded software solution to continuously monitor the skin/electrode impedance and alter the input impedance of the monitoring circuitry to adapt to the changing mismatch between the patient and the electronics. The present invention can be implemented in a continuous monitoring mode or time defined monitoring mode to allow either real-time implementation of the impedance matching or predefined matching based upon the accuracy required by the medical procedure. Furthermore, the hardware matching circuitry can be implemented to provide a user defined impedance matching resolution through the addition of more resistors in the resistor ladder network.
Therefore, there remains a need for an improved system and method to match skin impedance under varying conditions.